148 PRACTICAL ORGANIC CHEMISTRY tion indicates aniline. 2CBH3NH.NH.CCH5 = C0H6N:NC0H5= 2CGHi,NK, 2. Heat a small quantity with Fehling's solution and observe the formation of cuprous oxide. The hydrazobenzene is oxidised to azobenzene. Benzidine.—Five grams of powdered hydrazobenzene are shaken with 125 c.c. hydrochloric acid (3 per cent.) at 20—30°. In a quarter to half an hour the substance will have completely dis- solved. Finally, the mixture is heated to 45—50°, a little water added to redissolve any benzidine hydrochloride, and filtered warm. The benzidine is precipitated from the solution of the hydrochloride by adding to the cold solution an excess of caustic soda solution. It is filtered and washed free from alkali, and • recrystallised from boiling water or dilute alcohol. It crystallises in plates with nacreous lustre, m. p. 127°. C6H5NH.NHCGH5 - NH2C0H4.C0H4NH3. See Appendix, p. 275. PREPARATION 52. Phenylhydroxylamine, C0H5.NH.OH Bamberger, Ber., 1894, 27, 1548; Wohl, Ber., 1894, 27, 1432 ; Friedlander, Theerfarbenfabrikation, IV.. 48. 6 grins, ammonium chloride (in 200 c.c. water). 12 „ nitrobenzene. 18 ,, zinc dust. Mix the nitrobenzene and ammonium chloride solution in a. flask (i- litre). The zinc dust is added in portions of about a gram at a time with constant shaking or stirring by turbine, the tem- perature being maintained below 15°, by cooling if necessary in ice water. The addition of the zinc dust should take about an hour. The shaking is continued for another quarter of an hour, when the smell of nitrobenzene will have disappeared. The contents of the flask are filtered and washed with 100 c.c. water, so that the water trickles slowly through the filter. The filtrate is saturated with clean salt (80 grams) and cooled to o°. Colour- less crystals of phenylhydroxylamine fill the liquid. They are filtered at the pump, dried on a porous plate, and recrystallised if necessary from benzene. Yield C—8 grams.